 This oxidised the lead to litharge, and also oxidised other base metals present, the silver (and gold if present) remaining unoxidised.In the 18th century, the process was carried on using a kind of reverberatory furnace, but differing from the usual kind in that air was blown over the surface of the molten lead from bellows or (in the 19th century) blowing cylinders.The Pattinson process was patented by its inventor, Hugh Lee Pattinson, in 1833 who described it as "An improved method for separating silver from lead".